The present disclosure relates to optical coherence tomography, and in particular, to a beam-shaping optical probe for an optical coherence tomography probe having reduced back reflection.
Optical coherence tomography (OCT) is used to capture a high-resolution cross-sectional image of biological tissues and is based on fiber-optic interferometry. The core of an OCT system is typically a Michelson or Mach-Zehnder interferometer. For simplicity, only a basic Michelson interferometer is disclosed which typically includes a first optical fiber which is used as a reference arm and a second optical fiber which is used as a sample arm. The sample arm includes the sample to be analyzed, as well as a probe that contains optical components therein. A light source upstream of the probe provides light used in imaging. A photodetector is arranged in the optical path downstream of the sample and reference arms. The probe is used to direct light into and/or onto the sample and then to collect scattered light from the sample.
Optical interference of light from the sample arm and the reference arm is detected by the photodetector only when the optical path difference between the two arms is within the coherence length of the light from the light source. Depth information from the sample is acquired by axially varying the optical path length of the reference arm and detecting the interference between light from the reference arm and scattered light from the sample arm. A three-dimensional image is obtained by transversely scanning in two dimensions the optical path in the sample arm. The axial/depth range of the process is determined by the coherence length and spectral bandwidth, while the overall transverse resolution is dictated by the size of the image spot formed by the optical components of the probe.
Because the probe typically needs to be inserted into a small cavity of the body, generally it must be small and preferably have a simple optical design. Exemplary designs for the probe include a transparent cylinder in which the miniature probe optical components are contained and through which light is transmitted and received. However, light may be lost due to back reflection when it passes through materials having a different refractive index, thus decreasing image spot intensity. Additionally, unwanted back reflections decrease the signal to noise ratio in the data. Moreover, having multiple and separate optical components in the probe is generally problematic because the small optical components have to be assembled and aligned, which adds to the cost and complexity of manufacturing the probe.